The present invention relates to the use of precipitated amorphous silica or silicate as grinding aid for fish meal or fish food.
The consumption of fish has grown dramatically worldwide and especially in the United States and in Canada due to changes in the human diet during the last few years. As a result of the great demand for fish in the diet, hatcheries for different fish such as trout, herring, capelin, whitefish, catfish and particularly salmon have become more important.
It therefore becomes necessary to feed these fishes the most economical way. To accomplish this, it is standard practice to use the parts of fish which are not used for human consumption, such as bones, tails, heads, gill, etc., as part of the fish feed. The advantage of this practice is the high nutritional value of these parts as well as their low cost and abundance. These parts of the fish feed are called fish meal. Other parts of the final fish feed are, for example, corn cobs, grain, soy, minerals, vitamins and amino acids.
Another important area for fish meal is use as part of the diet for poultry.
The present invention provides fish meal or fish feed for consumption by fish and poultry. Fish feed normally is given to fish in the form of pellets, which are extruded. In order to extrude the fish feed, it is necessary to grind it into powder which can then be extruded. The usual grinding equipment is a hammer or disc mill. During this grinding process, as during all grinding processes, the temperature rises. This does not necessarily hamper a grinding process, but in the present case, the temperature increase is such that the fat content of the fish feed melts. As a result, the mill clogs, the operation has to be interrupted and the mill has to be cleaned.
Another problem which occurs is the increased tackiness of the milled product which tends to clog the sieves which are installed at the outlet side of the hammer mill. As a result, the opening of the sieves becomes smaller and the through-put of the mill is reduced.
A potential solution for this problem would be the use of a mill which can be cooled by a cooling liquid such as liquid nitrogen. These mills, however, are very expensive and the operation of these mills is uneconomical due to the cost of the cooling liquid.
The object of this invention was therefore, to find a cost efficient way to mill fish feed or fish meal without generating the problems of melting, clogging the apparatus, interrupting the process intermittently and to prevent the formation of tackiness in the product. I should be noted that the problems occur primarily with fish feed or fish meal which has a fat content of 5% or higher.